Thousands of people are killed or injured annually in automobile accidents wherein the vehicle driver and/or passengers are thrown forward as a result of the initial, i.e., primary, collision so as to impact against solid surfaces within the interior of the vehicle. As a result, passive restraint systems adapted for use with such vehicles have been developed for the purpose of reducing or eliminating these injuries and/or deaths.
One system which has been extensively investigated senses rapid vehicle deceleration, such as that which occurs upon a primary impact between an automobile and, for example, another vehicle. Upon receipt of a signal from the sensor, the system initiates inflation of an expandable passive restraint prior to the occurrence of any secondary collision between these individuals and the interior of the car. This restraint is interposed between the interior surface of the automobile and one or more occupants of the vehicle. The airbag restraint must therefore be inflated within milliseconds of the primary impact in order to ensure that the vehicle occupants' forward motion is arrested before injury occurs due to the secondary collisions against the adjacent solid interior surfaces.
Moreover, it is additionally desirable to ensure deflation of the restraining device as soon as the force of a crash is expended, so that the occupant(s) do not thereafter become trapped within the vehicle subsequent to the collision. In order to meet such criteria, specifications have been established whereby the expandable bag should be sufficiently inflated to restrain a vehicle occupant in about 30-60 milliseconds after initiation, with substantial deflation occurring after about 100 milliseconds.
Normally, such systems are activated by an inertial sensor switch responsive to the primary crash impact. The activation of this switch, in turn, results in the flow of a volume of gas sufficient to inflate a collapsed bag into a protective position in front of the driver or passenger. The inflating gas may be supplied from a source of compressed air or other compressed gas, such as that which is disclosed in Chute, U.S. Pat. No. 3,411,808 and Wissing et al., U.S. Pat. No. 3,413,013, and a number of other patents in the crash restraint field. Numerous other prior art patents (e.g., U.S. Pat. No. 3,880,447 to Thorn et al.; U.S. Pat. No. 4,068,862 to Ishi et al.; U.S. Pat. No. 4,711,466 to Breed; and U.S. Pat. Nos. 4,547,342; 4,561,675 and 4,722,551 to Adams et al.), disclose a system wherein the bag is inflated by igniting a pyrotechnic propellant composition and directing the gaseous combustion products produced thereby directly into the bag.
The first technique discussed above for inflating an air bag, i.e., utilizing a volume of compressed gas, requires a reservoir of such gas stored at a very high pressure, which may be discharged into the bag as soon as an impact is sensed by the inertial sensor switch. In order to ensure a sufficient volume of gas for inflating a motor vehicle air bag, however, a relatively large reservoir, at pressures of 3000 psi or more, is required. Moreover, to open the feed valve in the very short time interval required for ensuring the safety of the vehicle occupants, explosive arrangements are normally employed for bursting a diaphragm or cutting through a structural portion of the reservoir. As may be imagined, such explosive arrangements have significant inherent safety problems, such as the production of shrapnel by the explosion, as well as a propensity to promote hearing damage among the vehicle occupants due to the relatively high sound level reached within the passenger compartment as a result of the explosion. The psychological effect upon the vehicle occupants of having such explosives on board the automobile also cannot be ignored.
The gas bottle, i.e., reservoir, technique for inflating an air bag also suffers from a further disadvantage in that the gas pressure is highest at the commencement of bag deployment and decreases as a function of time as the gas in the storage reservoir is depleted. Moreover, the pressure/time history of such pressurized gas inflator devices is difficult if not impossible to control at reasonable cost and reliability.
In addition, the adiabatic cooling of the gas, as it expands from a storage condition of elevated pressure to the nearly ambient pressure of the inflatable bag, reduces the effective volume of the gas available for inflating the bag. This cooling effect thus requires the manufacturer of the device to provide a total gas storage volume significantly greater than that which would be required if the gas was initially stored at an elevated temperature. Furthermore, a minor leak can result in all of the gas being lost during the extended interim period that the passenger restraint system must remain in the automobile prior to any crash.
The second technique discussed above, employing a pyrotechnic gas generator, i.e., inflator device (these terms are used interchangably herein), utilizes a rapidly burning solid propellant composition stored within the inflator for producing a substantial volume of a hot gaseous product, which is then directed into an inflatable airbag. Some compositions are available which produce a sufficiently low temperature combustion gas such that the gas may be fed substantially directly into the bag without danger to the vehicle's occupants. Other systems produce a high temperature combustion product, requiring means for cooling the gas before it is introduced into the bag.
Many forms of gas generators or inflators utilizing combustible solid fuel gas generating compositions for the inflation of crash protection, i.e., "air bag", restraints, are known in the prior art. Commonly encountered features among such devices utilized for this purpose include: (1) an outer metal housing, e.g., of steel or aluminum, (2) a gas generant composition located within the housing, (3) means to ignite the gas generant responsive to a signal received from a sensor positioned at a location removed from the inflator, and (4) means to filter and to cool the gas, positioned between the propellant composition and a plurality of gas discharge ports or orifices defined by the generator housing.
Such pyrotechnic gas generators must be capable of withstanding enormous thermal and mechanical stresses for a short period during the gas generation process. Thus, most inflators that have been and are currently being used with automobile air bag devices are commonly fabricated using heavy gauge steel for the casing and other structural housing components, with these components being joined together by, for example, threaded screws, roll crimping or welding. The recent emphasis on weight reduction for the purpose of fuel conservation in motorized vehicles has, however, created a need and a demand for a lighter weight inflation system. One example of such a system is illustrated in U.S. Pat. No. 4,547,342 to Adams et al. disclosing an aluminum driver's side inflator unit.
Moreover, as is well understood by those practicing in this art, pyrotechnic inflators such as those described above may be fabricated and/or adapted in a variety of different configurations depending upon the particular response characteristics required for the intended application. One particularly important consideration in this regard is as to whether the inflator unit is to be mounted upon the steering wheel, in order to restrain the vehicle operator, or whether it is intended to protect, for example, the front seat passengers. In the latter case, the device is normally installed within the vehicle's dashboard. A different set of requirements must be met depending upon which mode of use is intended.
An inflator unit intended for installation on the driver's side, e.g., within the steering assembly, of an automobile must be smaller in size than a passenger side unit to enable it to fit within the steering wheel. It must additionally generate a gaseous combustion product up to two times faster than a passenger side unit due to the minimal separation between the driver and the steering wheel in comparison to the available space between the body of a passenger within the vehicle and the vehicle's dashboard. Moreover, a passenger side inflator device is required to produce up to four times as much gas as a driver's side inflator to completely inflate the correspondingly larger passenger side air bag. This increase in bag size is necessitated due to the relatively larger volume of space within the vehicle in which the passenger may be found, as opposed to the driver who is "locked" into a position behind the steering wheel. Numerous examples of such passenger side inflator devices are known in the prior art, such as that which is disclosed, for example, in U.S. Pat. No. 4,005,876 to Jorgensen et al.
An important additional consideration which must be addressed when designing a passenger side inflator device for installation within a motor vehicle is the presence of small children, either seated upon the lap of an adult passenger or located in a standing position between the dashboard of the vehicle and the front seat. In either case, it has been recognized that such children are liable to an increased risk of injury, notwithstanding the presence of an inflatable passive restraint device, due to the minimal degree of separation between the child's body and the air bag. This leads to a relative increase in the speed with which such children impact upon the passenger side air bag, thus greatly increasing their risk of injury in the event of a collision. Applicant is not aware of any apparatus or methodology available at present which is designed to prevent such injuries and/or deaths suffered by young children positioned within the vehicle as described above.